The present invention relates to an automotive seatbelt take-up device. More specifically, the present invention relates to a device that significantly reduces pressure applied by the seatbelt on the passenger when the seatbelt is worn.
Automotive seatbelts constrain passenger bodies to their seats to protect the passengers from collisions. A seatbelt take-up device includes a spiral spring used to take-up the seatbelt. When the seatbelt is to be secured, the seatbelt is drawn out in opposition to the spring force from the spiral spring, and a tongue is inserted into a buckle. The spiral spring biases the seatbelt in the take-up direction so that the seatbelt is tightened around the chest of the passenger, and the passenger feels pressure from the seatbelt. Thus, there is a need to reduce the take-up force from the seatbelt when the seatbelt is worn, thus easing the tightening at the chest, reducing the pressure felt by the passenger, and improving comfort.
Japanese patent publication number 60-30576 describes a take-up device implemented to reduce the seatbelt take-up force. Two spiral springs, one weak and one strong, having different elastic biasing forces, are connected in series. The weak and strong spiral springs are used when the seatbelt is drawn out or taken in. When the seatbelt is worn, the weak spring is used to reduce the take-up force. However, this take-up device uses two spiral springs, resulting in a complex structure having high production costs.
Japanese laid-open patent publication number 10-78786 proposes a seatbelt take-up device to reduce the take-up force when the seatbelt is worn. This conventional seatbelt take-up device has a spring clutch which provides a braking force to the take-up force of the spiral spring.
This conventional take-up device includes a shaft moving in tandem with a seatbelt take-up shaft; a spiral spring biasing the shaft in the take-up direction; a ratchet wheel restricted by a solenoid actuator to prevent rotation in the seatbelt take-up direction when the seatbelt is worn, and a spring clutch assembled along the shaft and the ratchet wheel. The spring clutch provides torque transfer for the clutch spring when the seatbelt is being taken up while being worn. By having the shaft move in tandem with the stopped ratchet wheel, the friction transfer provided by the clutch spring activates a braking force on the shaft, thus reducing the take-up force of the shaft.
In the latter seatbelt take-up device, the spring clutch provides a braking action via friction sliding of the clutch spring when the shaft rotates in the seatbelt take-up direction. However, the friction coefficient of the clutch spring varies greatly due to vibration in the automobile. This variation prevents stable braking action (stable take-up force reduction) and makes it difficult to reliably provide adequate pressure on the seatbelt.
Since the braking action is provided through friction sliding, there is an upper limit on the braking force. Increasing the spring force of the spiral spring to improve the seatbelt take-up performance is difficult. Furthermore, when the seatbelt is drawn out while it is being worn, the spring clutch is practically running in a loose state, with the ratchet wheel rotating as well. This prevents any reduction in the take-up force acting on the shaft. Thus, the seatbelt is drawn out in opposition to the strong take-up force of the spiral spring, resulting in higher pressure from the seatbelt. Furthermore, the rotation of the ratchet wheel generates ratchet noise.
It is an object of the present invention to provide an automotive seatbelt take-up device which overcomes the foregoing problems.
It is a further object of the present invention to reliably reduce the take-up force of the seatbelt after the seatbelt is secured to the passenger.
It is another object of the present invention to reduce both the drawing-out force and the take-up force of the seatbelt.
It is still a further object of the present invention to use the elastic force of the spring member to reduce both the drawing-out force and the take-up force of the seatbelt.
It is yet another object of the present invention to allow increased torque from a spiral spring.
Briefly stated, the present invention provides an automotive seatbelt take-up device has a primary spiral spring biasing a take-up shaft in a seatbelt take-up direction. A spring clutch transfers rotation of the take-up shaft in a seatbelt drawing-out direction to a ring. A secondary spiral spring is capable of generating rotational biasing forces on the take-up shaft in a direction opposite that of the primary spiral spring. Thus, the present invention provides an automotive seatbelt take-up device that can reduce both the drawing-out force and the take-up force of a seatbelt when the seatbelt is being worn.
According to an embodiment of the present invention, there is provided an automotive seatbelt take-up device includes a take-up shaft operating in tandem with an automotive seatbelt take-up shaft; a primary spiral spring fixed to the take-up shaft, biasing the take-up shaft in a take-up direction; and a balance spring capable of generating a rotational bias force in a direction opposite that of the primary spiral spring. The balance spring may be a secondary spiral spring roughly similar to the primary spiral spring with fewer windings, or, alternatively, the balance spring can be a torsion spring.
It is possible to have the rotational bias force generated by the balance spring (this is a rotational bias force going in the opposite direction from the primary spiral spring) act upon the take- up shaft when the seatbelt is secured to the passenger. If this is done, when the seatbelt is taken up after it is secured, the balance spring is wound tight so that the take-up force of the take-up shaft is reduced. If the seatbelt is subsequently drawn out, a release elastic force, releasing the balance spring that had been wound tight, assists the take-up shaft in the drawing-out direction.
According to another embodiment of the present invention, there is provided an automotive seatbelt take-up device includes a take-up shaft operating in tandem with an automotive seatbelt take-up shaft; a primary spiral spring fixed to the take-up shaft at its inner end portion and biasing the take-up shaft in a take-up direction; a spring clutch including a ring and a clutch spring fitted to the outside of the take-up shaft and transferring rotation in a seatbelt drawing-out direction to the ring; a balance spring capable of generating a rotational bias force in a direction opposite to that of the primary spiral spring, one end of the balance spring being fixed to the ring; and a ratchet wheel capable of using restricting means to restrict rotation in a seatbelt take-up direction, another end of the balance spring being fixed to the ratchet wheel.
The balance spring here can be, for example, a secondary spiral spring similar to the primary spiral spring with fewer windings (e.g., around 3-10 windings). Alternatively, a torsion spring similar to this secondary spiral spring can be used as the balance spring.
The restricting means is not activated until the seatbelt is secured to the passenger, and the balance spring is in a free state since the ratchet wheel can rotate freely. When the seatbelt is secured to the passenger and the tongue and buckle are connected, restricting means restricts rotation of the ratchet wheel so that it cannot rotate in the take-up direction. When slack in the seatbelt is to be taken up from this state, the friction transfer provided by the spring clutch is used to transfer the rotation of the take-up shaft to the ring, rotating the ring so that the balance spring is wound tight. In this manner, the take-up force of the take-up shaft is reliably reduced by the tightly wound state of the balance spring, and the passenger is only weakly constrained by the seatbelt.
When the seatbelt is worn and the passenger""s body is moved to draw out the seatbelt, the spring clutch is in a transferring state so that the release elastic force of the balance spring assists the take-up shaft. Thus, the passenger is only weakly constrained by the seatbelt. Next, when the passenger""s body returns to its original position and the seatbelt needs to be taken up, the friction transfer provided by the spring clutch causes the balance spring to be wound tightly, as described above, and the take-up force of the take-up shaft is reduced by the tightly wound state of the balance spring. This state results in the passenger being only weakly constrained by the seatbelt.
When the seatbelt is to be removed from the passenger""s body and the tongue is removed from the buckle, the restriction provided by restricting means on the ratchet wheel is released and the ratchet wheel is allowed to rotate freely. Thus, with the balance spring in a free state, the seatbelt is rapidly and firmly taken in by the take-up force of the primary spiral spring.
According to a feature of the present invention, there is provided an automotive seatbelt take-up device as described above wherein, when the seatbelt is being worn by a passenger and the take-up shaft rotates in the take-up direction while the ratchet wheel applies rotation restriction, the spring clutch provides friction transfer to wind the balance spring tight, thus reducing take-up force from the take-up shaft. Generally, slack in the seatbelt is taken up after the seatbelt is secured to the passenger. When the take-up shaft is rotated in the take-up direction while the ratchet wheel is restricted, the friction transfer provided by the spring clutch winds the balance spring tightly and reduces the take-up force of the take-up shaft.
According to another feature of the present invention, there is provided an automotive seatbelt take-up device as described above wherein, when the seatbelt is being worn and the seatbelt is drawn out while the ratchet wheel applies rotation restriction, a release elastic force of the balance spring assists, by way of the spring clutch, the take-up shaft in the drawing-out direction.
When the passenger""s body moves while the seatbelt is secured, the seatbelt is drawn out. Since the balance spring is wound tight up to this point, as described above, when the seatbelt is drawn out, the release elastic force of the balance spring can, via the spring clutch, assist the take-up shaft in the drawing-out direction. Thus, the passenger experiences only a weak constraining force.
According to a further feature of the present invention there is provided an automotive seatbelt take-up device as described above wherein, when the seatbelt is taken up after being drawn out, the spring clutch provides friction transfer to wind the balance spring tight, thus reducing take-up force of the take-up shaft. When the seatbelt is to be taken up after it is drawn out, as described above, the friction transfer of the spring clutch winds the balance spring tightly, thus reducing the take-up force of the take-up shaft.
According to another feature of the present invention, there is provided an automotive seatbelt take-up device as described above, wherein the balance spring is a spiral spring. Since the balance spring is a spiral spring, the balance spring can be mounted. for example, between the ring and the ratchet wheel. This provides a more compact take-up device.
According to another feature of the present invention, there is provided an automotive seatbelt take-up device as described above, wherein the balance spring is a torsion spring. Since the balance spring is a torsion spring, the production cost of the balance spring is reduced.